Possible neutron halo in triaxial nucleus 42Al

TL;DR

This paper introduces a microscopic triaxial relativistic Hartree-Bogoliubov theory in continuum to explore neutron halo phenomena in aluminum isotopes, predicting a possible halo in 42Al with unique shape decoupling.

Contribution

It develops a comprehensive theoretical framework that accounts for triaxiality, pairing, and continuum effects, and applies it to predict novel halo features in 42Al.

Findings

Predicted 42Al to be triaxially deformed with a possible neutron halo.

Density distribution suggests a neutron halo extending far from the core.

Discovered exchange of axes between triaxial core and halo.

Abstract

A microscopic self-consistent triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc), which simultaneously takes into account the triaxiality and pairing correlations as well as continuum effects, is established and applied to explore the novel halo phenomenon in aluminum isotopes. The experimental proton drip line and the available data of neutron separation energies and charge radii are reproduced well without any free parameters. The neutron-richest odd-odd aluminum isotope observed so far, 42Al, is predicted to be triaxially deformed with beta=0.35 and gamma=42. Its one-neutron separation energy is predicted to be 0.68 MeV, in agreement with the AME2020, and the neutron rms radius is 3.94 fm, remarkably larger than the empirical value. The density distribution of the valance neutron, which extends much farther in space than the core, suggests a possible neutron halo in 42Al. The dominant components responsible for the spatial extension of the halo are revealed by the single-neutron orbitals around the Fermi energy. A novel phenomenon, the exchange of the intermediate and short axes between the triaxial core with beta=0.38 and gamma=50, and the triaxial halo with beta=0.79 and gamma=-23, is found. Future experiments to explore the halo phenomenon and the novel shape decoupling in 42Al are highly demanded.